An RGSC beamformer is known from Wolfgang Herbordt: “Combination of Robust Adaptive Beamforming with Acoustic Echo Cancellation for Acoustic Human/Machine Interface”, Dissertation, Friedrich-Alexander University Erlangen/Nuremberg, submitted 03.12.2003, page 99 ff.
A system and method for picking up audio signals is known from US 2005/0047611 A1, with which a microphone array is used to reduce an interference signal compared to a useful signal. To this end the microphones of the microphone array are connected to a beamformer by way of a filter unit and a summation element. In the case of the mentioned document, the filter unit of the beamformer is also referred to in an unconventional manner as a calibration filter.
In general in the case of a beamformer a number of microphones are connected together to form a microphone system, having a directional characteristic. This causes acoustic input signals in the microphone system to be dampened to varying degrees as a function of their direction of incidence into the microphone system. In the case of a beamformer the signal transmission functions of the microphones used have to be tuned very precisely to each other, in order to be able to achieve the desired directional effect. Deviations in the signal transmission functions due to tolerances or ageing effects significantly impair the function of the beamformer, such that it may no longer be possible to ensure a desired interference noise suppression to an adequate degree with the microphone system used. This applies in particular to beamformers with microphone arrays with a very small aperture, as used for example in hearing device applications, in which differential or superdirective beamformer algorithms are frequently used.
It is known that calibration filters can be connected downstream from the microphones of a beamformer, to compensate for component tolerances in the microphones used. The signal transmission response of the microphones is determined once and filter coefficients of calibration filters, connected downstream from the microphones, are set such that the component tolerances are equalized. However this procedure has the disadvantage that ageing effects cannot be taken into account.